Lithium cobalt oxide for a lithium secondary battery and lithium secondary battery comprising positive electrode including the same

ABSTRACT

A cobalt oxide for a lithium secondary battery, a method of preparing the cobalt oxide; a lithium cobalt oxide for a lithium secondary battery formed from the cobalt oxide; and a lithium secondary battery having a positive electrode including the lithium cobalt oxide, the cobalt oxide having a tap density of about 2.8 g/cc to about 3.0 g/cc, and an intensity ratio of about 0.8 to about 1.2 of a second peak at 2θ of about 31.3±1° to a first peak at 2θ of about 19±1° in X-ray diffraction spectra, as analyzed by X-ray diffraction.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a divisional application based on pending application Ser. No.15/702,048, filed Sep. 12, 2017, the entire contents of which is herebyincorporated by reference.

Korean Patent Application No. 10-2016-0118208, filed on Sep. 13, 2016,and Korean Patent Application No. 10-2017-0115909, filed on Sep. 11,2017, in the Korean Intellectual Property Office, and entitled: “CobaltOxide for Lithium Secondary Battery, Preparing Method Thereof, LithiumCobalt Oxide Formed From the Cobalt Oxide, and Lithium Secondary BatteryHaving Positive Electrode Comprising the Lithium Cobalt Oxide,” isincorporated by reference herein in its entirety.

BACKGROUND 1. Field

Embodiments relate to a cobalt oxide for a lithium secondary battery, amethod of preparing the same, a lithium cobalt oxide formed from thecobalt oxide, and a lithium secondary battery having a positiveelectrode including the lithium cobalt oxide.

2. Description of the Related Art

High-voltage lithium secondary batteries with high energy density may beused in a variety of applications. For example, in the field of electricvehicles (including hybrid electric vehicles (HEVs) and plug-in hybridelectric vehicles (PHEVs)), a lithium secondary battery operable at ahigh temperature with good discharge capacity to charge and discharge alarge quantity of electricity may be used.

SUMMARY

The embodiments may be realized by providing a cobalt oxide for alithium secondary battery, the cobalt oxide having a tap density ofabout 2.8 g/cc to about 3.0 g/cc, and an intensity ratio of about 0.8 toabout 1.2 of a second peak at 2θ of about 31.3±1° to a first peak at 2θof about 19±1° in X-ray diffraction spectra, as analyzed by X-raydiffraction.

The cobalt oxide may have an average particle diameter (D50) of about 15μm to about 18 μm, a particle diameter (D90) of about 23 μm to about 25μm, and a particle diameter (D10) of about 5 μm to about 7 μm.

The cobalt oxide may have a tap density of about 2.8 g/cc to about 3.0g/cc.

The embodiments may be realized by providing a method of preparing thecobalt oxide for a lithium secondary battery according to an embodiment,the method including performing a precipitation reaction of a mixtureincluding a cobalt precursor and a precipitant, and the precipitationreaction is carried out under an oxidizing gas atmosphere to obtain thecobalt oxide.

The method may further include washing and sieving a reaction productafter the reacting under the oxidizing gas atmosphere.

The precipitation reaction of the mixture may be performed at a pH ofabout 11.0 to about 12.0 and a temperature of about 60° C. to about 80°C.

The cobalt precursor may be cobalt sulfate.

The embodiments may be realized by providing a lithium cobalt oxide fora lithium secondary battery, the lithium cobalt oxide being representedby Formula 1 and having a spherical particle shape, a pellet density ofabout 3.98 g/cc to about 4.2 g/cc, an average particle diameter (D50) ofabout 23 μm to about 28 μm, a particle diameter (D90) of about 35 μm toabout 45 μm, and a particle diameter (D10) of about 10 μm to about 13μm:Li_(a)Co_(b)O_(c)   [Formula 1]

wherein, in Formula 1, 0.9≤a≤1.1, 0.98≤b≤1.00, and 1.9≤c≤2.1.

The lithium cobalt oxide may further include at least one selected frommagnesium (Mg), calcium (Ca), strontium (Sr), titanium (Ti), zirconium(Zr), boron (B), aluminum (Al), and fluorine (F).

The embodiments may be realized by providing a lithium secondary batterycomprising a positive electrode that includes the lithium cobalt oxideaccording to an embodiment.

The positive electrode may have a density of about 4.05 g/cc to about4.15 g/cc.

BRIEF DESCRIPTION OF THE DRAWINGS

Features will be apparent to those of skill in the art by describing indetail exemplary embodiments with reference to the attached drawings inwhich:

FIG. 1A illustrates a schematic view of a lithium secondary batteryaccording to an embodiment;

FIG. 1B illustrates a flowchart of a method of preparing a lithiumcobalt oxide according to an embodiment;

FIG. 1C illustrates a flowchart of a comparative method of preparing alithium cobalt oxide;

FIGS. 2A and 2B illustrate graphs showing results of X-ray diffractionanalysis on cobalt oxides (Co₃O₄) prepared in Example 1 and ComparativeExample 1, respectively;

FIG. 3 illustrates a graph showing density with respect to pressing gapof positive electrodes manufactured in Manufacture Example 1 andComparative Manufacture Example 1;

FIG. 4 illustrates a graph showing capacity retention with respect tothe number of cycles in a lithium secondary battery manufactured inManufacture Example 1;

FIGS. 5A to 5C illustrate scanning electron microscope (SEM) images ofthe cobalt oxide prepared in Example 1; and

FIGS. 6A and 6B illustrate SEM images of the cobalt oxide prepared inComparative Example 1.

DETAILED DESCRIPTION

Example embodiments will now be described more fully hereinafter withreference to the accompanying drawings; however, they may be embodied indifferent forms and should not be construed as limited to theembodiments set forth herein. Rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey exemplary implementations to those skilled in the art.

In the drawing figures, the dimensions of layers and regions may beexaggerated for clarity of illustration. It will also be understood thatwhen a layer or element is referred to as being “on” another layer orelement, it can be directly on the other layer or element, orintervening layers may also be present. In addition, it will also beunderstood that when a layer is referred to as being “between” twolayers, it can be the only layer between the two layers, or one or moreintervening layers may also be present. Like reference numerals refer tolike elements throughout.

As used herein, the terms “or” and “and/or” includes any and allcombinations of one or more of the associated listed items. Expressionssuch as “at least one of,” when preceding a list of elements, modify theentire list of elements and do not modify the individual elements of thelist.

Hereinafter, example embodiments of a cobalt oxide for a lithiumsecondary battery, a method of preparing the cobalt oxide, a lithiumcobalt oxide formed from the cobalt oxide, and a lithium secondarybattery having a positive electrode including the lithium cobalt oxidewill be described in greater detail.

According to an aspect of the present disclosure, there is provided acobalt oxide (Co₃O₄) for a lithium secondary battery. The cobalt oxidemay have, e.g., a tap density of about 2.8 g/cc to about 3.0 g/cc, andan intensity ratio of about 0.8 to about 1.2 of a second peak at 2θ ofabout 31.3±1° to a first peak at 2θ of about 19±1° in X-ray diffractionspectra, as analyzed by X-ray diffraction.

The first peak and the second peak may correspond to the (111) crystalplane and (220) crystal plane of the cobalt oxide, respectively.

For example, the intensity ratio of the second peak to the first peakmay be 1.0.

A cobalt oxide as a precursor of lithium cobalt oxide may be smallparticles having an average particle diameter of about 5 μm to about 7μm. When such a cobalt oxide is used to form a lithium cobalt oxidehaving a large particle diameter, a lithium precursor such as lithiumcarbonate, lithium hydroxide, or the like may be used in an excess ofabout 1.04 to 1.05 mole with respect to 1 mole of the cobalt oxide. Whensuch an excess of a lithium precursor is used, a process of removingexcess lithium may be performed, causing preparation cost increase ofthe lithium cobalt oxide.

A lithium cobalt oxide may be obtained according to a comparativepreparation method illustrated in FIG. 1C. First, a cobalt oxide (Co₃O₄)may be prepared by thermally treating CoOOH obtained by co-precipitationreaction. A lithium precursor may be added to the prepared cobalt oxideand thermally treated to obtain a lithium cobalt oxide, which may thenbe ground, followed by a post-treatment process to remove residuallithium and a sieving process.

Referring to FIG. 1B, a method of preparing a lithium cobalt oxideaccording to an embodiment may include preparing a cobalt oxide (Co₃O₄)through a precipitation reaction of a cobalt precursor, and oxygen isinjected to accelerate oxidation during the precipitation reaction.Lithium cobalt oxide is prepared by adding a lithium precursor to theprepared cobalt oxide and heat-treating the resultant.

A cobalt oxide (Co₃O₄) according to an embodiment may be prepared byoxidation precipitation, without need to perform thermal treatment,unlike cobalt oxide prepared using a thermal treatment as describedabove with reference to FIG. 1C, thus reducing preparation cost. Nothermal treatment may be performed, and a pore-free, high-density cobaltoxide may be obtained. Using this high-density cobalt oxide, anelectrode with improved electrode density may be prepared.

Next, the cobalt oxide may be mixed with a lithium precursor and thenthermally treated to obtain a target lithium cobalt oxide of Formula 1.The amounts of the cobalt oxide and the lithium precursor may bestoichiometrically adjusted to obtain the target lithium cobalt oxide ofFormula 1. Just a stoichiometric, non-excess amount of the lithiumprecursor, required to form the target compound, may be added. Forexample, when the target lithium cobalt oxide of Formula 1 is LiCoO₂,the cobalt oxide and a lithium precursor may be used, e.g., in a molarratio of about 1:1. The lithium cobalt oxide prepared may be subjectedto grinding and sieving processes.

In an implementation, the cobalt oxide may have an average particlediameter (D50) of about 15 μm to about 18 μm, e.g., about 15 μm to about17 μm. The cobalt oxide according to an embodiment may have a relativelylarge average particle diameter within these ranges, and a lithiumcobalt oxide having a large particle diameter may be easily preparedfrom the cobalt oxide, without addition of an excess of a lithiumprecursor as used to prepare other lithium cobalt oxides. In animplementation, the cobalt oxide may have, e.g., a particle diameter(D90) of about 23 μm to about 25 μm and a particle diameter (D10) ofabout 5 μm to about 7 μm.

An intensity ratio of a second peak at 2θ of 31.3±1° to a first peak at2θ of 19±1° in X-ray diffraction spectra gives information about a ratioof Co³⁺ and Co³⁺ in the cobalt oxide (Co₃O₄). In an implementation, anatomic ratio of Co³⁺ (tet) to Co³⁺ (oct) in the cobalt oxide (Co₃O₄) maybe about 1:2.1 to about 1:2.25.

In an implementation, a lithium cobalt oxide formed from the cobaltoxide may have a pellet density of about 3.98 g/cc to about 4.2 g/cc.The cobalt oxide may have a high tap density, e.g., of about 2.8 g/cc toabout 3.0 g/cc. When the cobalt oxide has a pellet density and a tapdensity within these ranges, an electrode having good densitycharacteristics may be prepared.

A positive electrode formed using a lithium cobalt oxide according to anembodiment may have a desirable density, e.g., of about 4.05 g/cc toabout 4.15 g/cc. Using this positive electrode with the above-describedelectrode density, a lithium secondary battery with improved lifetimecharacteristics and rate characteristics may be manufactured. If thedensity of an electrode plate is only increased by, e.g., excessivepressing without increasing the tap density of a cobalt oxide and thepellet density of a lithium cobalt oxide prepared therefrom,impregnation of electrolyte may not be sufficient and/or the electrodeplate may be broken, thus leading to deterioration in lifetime andelectrochemical characteristics of a lithium secondary battery. A cobaltoxide according to any of the above-described embodiments may have animproved (e.g., higher) tap density, and a lithium cobalt oxideaccording to any of the above-described embodiments may have an improved(e.g., higher) pellet density, and thus may help prevent theabove-described drawbacks when subjected to pressing. The lithium cobaltoxide may also have improved electrochemical characteristics.

A lithium cobalt oxide according to any of the embodiments may beprepared using an appropriate, non-excess amount of a lithium precursor,and a residual lithium (that could otherwise result from use of excesslithium precursor) may be less present in the lithium cobalt oxide. Theamount of the residual lithium in a lithium cobalt oxide according toany of the embodiment may be, e.g., 500 ppm or less, as measured bytitration.

In an implementation, the lithium cobalt oxide may have, e.g., anaverage particle diameter (D50) of about 23 μm to about 28 μm, aparticle diameter (D90) of about 35 μm to about 45 μm, and a particlediameter (D10) of about 10 μm to about 13 μm.

As used herein, the terms “D50”, “D90”, and “D10” may refer to particlediameters corresponds 50%, 90%, and 10% by volume, respectively, of acumulative distribution curve of particles accumulated from smallest tolargest in particle size (diameter) with respect to a 100% total volumeof the accumulated particles.

In an implementation, a lithium cobalt oxide may be a compound having aspherical particle shape represented by Formula 1, a pellet density ofabout 3.98 g/cc to about 4.2 g/cc, an average particle diameter (D50) ofabout 23 μm to about 28 μm, a particle diameter (D90) of about 35 μm toabout 45 μm, and a particle diameter (D10) of about 10 μm to about 12μm.Li_(a)Co_(b)O_(c)   [Formula 1]

In Formula 1, 0.9≤a≤1.1, 0.98≤b≤1.00, and 1.9≤c≤2.1.

In an implementation, the lithium cobalt oxide may have a high pelletdensity, a spherical particle shape with improved sphericity, and thusreduced specific surface area. Using such a lithium cobalt oxideaccording to an embodiment, a positive electrode with improved chemicalstability under high-temperature charge and discharge conditions may bemanufactured. A lithium secondary battery with improved capacity andrate characteristics may also be manufactured using the positiveelectrode.

If the pellet density of the lithium cobalt oxide were to be outside ofthe above range, a lithium secondary battery having a positive electrodeincluding the lithium cobalt oxide could have reduced rate and capacitycharacteristics.

In an implementation, the lithium cobalt oxide represented by Formula 1may be LiCoO₂.

In an implementation, the lithium cobalt oxide may further include atleast one element selected from, e.g., magnesium (Mg), calcium (Ca),strontium (Sr), titanium (Ti), zirconium (Zr), boron (B), aluminum (Al),and fluorine (F). Using a positive electrode manufactured with a lithiumcobalt oxide further including at least one of these elements, a lithiumsecondary battery with further improved electrochemical characteristicsmay be manufactured.

Hereinafter, embodiments of a method of preparing a cobalt oxide for alithium secondary battery will be described in greater detail.

A precipitation reaction of a mixture including a cobalt precursor,e.g., a cobalt sulfate, a precipitant, and a solvent is carried out, andan oxygen is injected to accelerate oxidation during the precipitationreaction. As such, the precipitation reaction is carred out under anoxidizing gas atmosphere.

A chelating agent may optionally be further added into the mixtureduring the precipitation reaction. The chelating agent may be anychelating agent commonly used in the art. For example, the chelatingagent may include ammonia, ammonium sulfate, or the like.

The precipitation reaction may be performed at a temperature of about60° C. to about 80° C. When the precipitation reaction is performedwithin this temperature range, a cobalt oxide with improved densitycharacteristics may be obtained.

The pH of the mixture may be adjusted within a range of about pH 11 topH 12. When the mixture has a pH within this range, a cobalt oxidesatisfying target particle conditions may be obtained.

The precipitant as a pH adjusting agent of the mixture may include,e.g., a sodium hydroxide solution, sodium carbonate solution, ammoniumbicarbonate (NH₄HCO₃) solution, or the like.

The solvent may include, e.g., water. The amount of the solvent may befrom about 100 parts to about 3,000 parts by weight, based on 100 partsby weight of the cobalt precursor. When the amount of the solvent iswithin this range, a uniform mixture of the ingredients may be obtained.

The cobalt oxide according to an embodiment obtained through theabove-described processes may have improved pellet density, compared toa cobalt oxide prepared by a conventional method. Using the cobalt oxideaccording to an embodiment, a high-density lithium cobalt oxide having alarge particle diameter may be obtained. Using this lithium cobaltoxide, a positive electrode with improved electrode density may bemanufactured.

A method of preparing a lithium cobalt oxide from the cobalt oxideprepared according to the above-described process will be described asfollows.

After the cobalt oxide may be mixed with a lithium precursor to obtain amixture, the mixture may be thermally treated.

The lithium precursor may include, e.g., lithium hydroxide, lithiumfluoride, lithium carbonate, or a mixture thereof. The amount of thelithium precursor may be stoichiometrically controlled to obtain alithium cobalt oxide of Formula 1. For example, when a target lithiumcobalt oxide, i.e., the lithium cobalt oxide of Formula 1, is LiCoO₂,the amount of the lithium precursor may be about 1.0 mole with respectto 1 mole of the cobalt oxide.

The thermal treatment may be performed at a temperature of about 1,000°C. to about 1,200° C. When the thermal treatment temperature is withinthis range, a lithium cobalt oxide with improved pellet density may beobtained.

The resulting product from the thermal treatment may be ground and thensieved to obtain a lithium cobalt oxide having a target average particlediameter and a target pellet density.

In an implementation, the lithium cobalt oxide may have, e.g., anaverage particle diameter (D50) of about 23 μm to about 28 μm, aparticle diameter (D90) of about 35 μm to about 45 μm, and a particlediameter (D10) of about 10 μm to about 12 μm.

Hereinafter, a method of preparing a lithium secondary battery using alithium cobalt oxide according to any of the above-described embodimentsas a positive active material will be described in detail. For example,a method of manufacturing a lithium secondary battery including apositive electrode, a negative electrode, a lithium salt-containingnon-aqueous electrolyte, and a separator will be described as anembodiment.

The positive electrode and the negative electrode may be formed bycoating a positive active material layer composition and a negativeactive material layer composition, respectively, on current collectors,and then drying the resulting products.

The positive active material layer composition may be prepared by mixinga positive active material, a conducting agent, a binder, and a solvent,wherein the lithium cobalt oxide according to any of the above-describedembodiments may be used as the positive active material. The amount ofthe positive active material may be in a range of about 1 part to about50 parts by weight, based on 100 parts by weight of the positive activematerial layer composition.

The binder may facilitate binding of an active material to a conductingagent and/or to a current collector. Examples of the binder may includepolyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose(CMC), starch, hydroxypropylcellulose, reproduced cellulose,polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene,polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonatedEPDM, styrene-butadiene rubber, fluororubber, and various copolymers.The amount of the binder may be in a range of about 2 parts to about 5parts by weight, based on 100 parts by weight of the positive activematerial layer composition. When the amount of the binder is within thisrange, a binding force of the positive active material layer to thecurrent collector may be satisfactorily strong.

The conducting agent may include a suitable material that has anappropriate conductivity without causing chemical changes in thefabricated battery. Examples of the conducting agent may includegraphite such as natural graphite or artificial graphite; carbonaceousmaterials such as carbon black, acetylene black, Ketjen black, channelblack, furnace black, lamp black, or summer black; conductive fiberssuch as carbon fibers or metal fibers; metallic powder such as aluminumpowder, or nickel powder; fluorinated carbon powder; conductive whiskerssuch as zinc oxide or potassium titanate; conductive metal oxides suchas a titanium oxide; and a conductive material such as polyphenylenederivatives.

The amount of the conducting agent may be in a range of about 2 parts toabout 5 parts by weight, based on 100 parts by weight of the positiveactive material layer composition. When the amount of the conductingagent is within this range above, a finally obtained positive electrodemay have improved conductivity characteristics.

An example of the solvent may include N-methylpyrrolidone.

The amount of the solvent may be in a range of about 10 part to about200 parts by weight, based on 100 parts by weight of the positive activematerial. When the amount of the solvent is within this range, formingthe positive active material layer may be facilitated.

The positive current collector may have a suitable thickness, e.g., in arange of about 3 μm to about 500 μm, so long as a material forming thepositive current collector has high conductivity without causing achemical change in a battery. For example, the positive currentcollector may be formed of stainless steel, aluminum, nickel, titanium,heat-treated carbon, or aluminum, or stainless steel that issurface-treated with carbon, nickel, titanium, silver, or the like. Thepositive current collector may have an uneven surface with fineirregularities to improve a binding force with the positive activematerial, and may have any of various forms, including a film, a sheet,a foil, a net, a porous body, a foam, and a non-woven fabric.

The negative active material layer composition may be prepared by mixinga negative active material, a binder, a conducting agent, and a solventtogether.

The negative active material may be a material that allows intercalationand deintercalation of lithium ions. Examples of the negative activematerial may include a carbonaceous material such as graphite andcarbon; lithium metal and an alloy thereof; and a silicon oxide-basedmaterial. In an implementation, the negative active material may includesilicon oxide.

The amount of the binder may be in a range of about 1 part to about 50parts by weight, based on 100 parts by weight of the negative activematerial layer composition. Examples of the binder may be the same asthose listed above in connection with the preparation of the positiveelectrode.

The amount of the conducting agent may be in a range of about 1 part toabout 5 parts by weight, based on 100 parts by weight of the negativeactive material layer composition. When the amount of the conductingagent is within this above range, a finally obtained negative electrodemay have improved conductivity characteristics.

The amount of the solvent may be in a range of about 10 part to about200 parts by weight, based on 100 parts by weight of the negative activematerial. When the amount of the solvent is within this range, formingthe negative active material layer may be facilitated.

Examples of the conducting agent and the solvent used herein may be thesame as those listed above in connection with the preparation of thepositive electrode.

A negative current collector may have a suitable thickness, e.g., in arange of about 3 μm to about 500 μm, so long as a material forming thenegative current collector has conductivity without causing a chemicalchange in a battery. For example, the negative current collector may beformed of copper, stainless steel, aluminum, nickel, titanium,heat-treated carbon, or copper, or stainless steel that issurface-treated with carbon, nickel, titanium, silver, or the like. Inaddition, similar to the positive current collector, the negativecurrent collector may have an uneven surface with fine irregularities toimprove a binding force with the negative active material, and may haveany of various forms, including a film, a sheet, a foil, a net, a porousbody, a foam, and a non-woven fabric.

Then, a separator may be disposed between the positive electrode and thenegative electrode fabricated according to the above-describedprocesses.

The separator may have a pore diameter in a range of about 0.01 μm toabout 10 μm and a thickness in a range of about 5 μm to about 300 μm.Examples of the separator may include an olefin-based polymers such aspolypropylene or polyethylene; or sheets or non-woven fabric formed ofglass fiber. When a solid electrolyte, e.g., a polymer electrolyte isused, the solid electrolyte may also serve as the separator.

The lithium salt-containing non-aqueous electrolyte may include anon-aqueous electrolyte and a lithium salt. The non-aqueous electrolytemay be, e.g., a non-aqueous liquid electrolyte, an organic solidelectrolyte, or an inorganic solid electrolyte.

In an implementation, the non-aqueous liquid electrolyte may include,e.g., an aprotic organic solvent, for example, N-methyl-2-pyrrolidone,propylene carbonate, ethylene carbonate, butylene carbonate, dimethylcarbonate, diethyl carbonate, gamma-butyrolactone, 1,2-dimethoxyethane,2-methyl tetrahydrofuran, dimethylsulfoxide, 1,3-dioxolane, formamide,N,N-dimethylformamide, acetonitrile, nitromethane, methyl formate,methyl acetate, trimethoxy methane, a dioxolane derivative, sulfolane,methylsulfolane, 1,3-dimethyl-2-imidazolidinone, a propylene carbonatederivative, a tetrahydrofuran derivative, ether, methyl propionate, orethyl propionate.

Examples of the organic solid electrolyte may include a polyethylenederivative, a polyethylene oxide derivative, a polypropylene oxidederivative, a phosphoric acid ester polymer, polyvinyl alcohol, andpolyfluoride vinylidene.

Examples of the inorganic solid electrolyte may include Li₃N, LiI,Li₅NI₂, Li₃N—LiI—LiOH, Li₂SiS₃, Li₄SiO₄, Li₄SiO₄—LiI—LiOH, andLi₃PO₄—Li₂S—Si S₂.

In an implementation lithium salt as a material dissoluble in anon-aqueous electrolyte may include, e.g., LiCl, LiBr, LiI, LiClO₄,LiBF₄, LiB₁₀Cl₁₀, LiPF₆, LiCF₃SO₃, LiCF₃CO₂, LiAsF₆, LiSbF₆, LiAlCl₄,CH₃SO₃Li, (CF₃SO₂)₂NLi, (FSO₂)₂NLi, lithium chloroborate, or loweraliphatic lithium carboxylate.

FIG. 1 illustrates a schematic cross-sectional view of a structure of alithium secondary battery 10 according to an embodiment.

Referring to FIG. 1, the lithium secondary battery 10 according to anembodiment may include a positive electrode 13; a negative electrode 12;a separator 14 between the positive electrode 13 and the negativeelectrode 12; an electrolyte impregnated into the positive electrode 13,the negative electrode 12, and the separator 14; a battery case 15; anda cap assembly 16 sealing the battery case 15. In an implementation, thelithium secondary battery 10 may be manufactured by sequentiallystacking the positive electrode 13, the separator 14, the negativeelectrode 12 in this stated order to form a stack, winding this stackinto a spiral form, and encasing the wound stack into the battery case15. The battery case 15 may then be sealed with the cap assembly 16,thereby completing manufacturing of the lithium secondary battery 10.

The following Examples and Comparative Examples are provided in order tohighlight characteristics of one or more embodiments, but it will beunderstood that the Examples and Comparative Examples are not to beconstrued as limiting the scope of the embodiments, nor are theComparative Examples to be construed as being outside the scope of theembodiments. Further, it will be understood that the embodiments are notlimited to the particular details described in the Examples andComparative Examples.

Example 1 Preparation of Cobalt Oxide and Lithium Cobalt Oxide

An about 1.5 M cobalt sulfate aqueous solution, and a 3.0 M NaOH aqueoussolution as a precipitant were prepared and then put at the same timeinto a reactor to obtain a reaction mixture. After a pH adjustment ofthe reaction mixture to about pH 11.5, a precipitation reaction wascarried out at about 70° C. In order to facilitate oxidation during theprecipitation reaction, oxygen was fed into the mixture of theprecipitation reaction in a continuous flow stirred-tank reactor (CSTR).The CSTR does not refer to the reactor itself, but rather to thecontinuous stirred reaction type.

As a result of these processes, spherical Co₃O₄ having an averageparticle diameter (D50) of about 15 μm was obtained. This sphericalCo₃O₄ was washed repeatedly with deionized water using a centrifugeuntil the amount of SO₄ reached about 100 ppm or less, followed bysieving through a sieve having an about 270 mesh size to obtain ahigh-density cobalt oxide (Co₃O₄).

The obtained cobalt oxide and lithium carbonate were dry-mixed in amolar ratio of Co:Li of about 1:1 with a mixer for about 5 minutes, andthen thermally treated at about 1,100° C. for about 10 hours to obtain alithium cobalt oxide (LiCoO₂). After the thermal treatment, theresulting lithium cobalt oxide was ground by jet milling at about 2,000rpm and then sieved through a sieve having an about 325 mesh size.

Example 2

Cobalt oxide (Co₃O₄) and lithium cobalt oxide (LiCoO₂) were obtained inthe same manner as in Example 1, except that the temperature of theprecipitation reaction for preparing the cobalt oxide was changed toabout 80° C.

Comparative Example 1

An about 1.5 M cobalt sulfate aqueous solution, a 3.0 M NH₄HCO₃ aqueoussolution as a precipitant, and a NH₄OH aqueous solution as a chelatingagent were prepared and then put at the same time into a reactor toobtain a reaction mixture. After a pH adjustment of the reaction mixtureto about pH 11.5, a precipitation reaction was carried out at about 40°C. to obtain CoOOH as a precipitate.

The obtained precipitate was filtered, washed, and dried overnight atabout 120° C. to obtain cobalt oxide (Co₃O₄).

The cobalt oxide was thermally treated at about 800° C. (first thermaltreatment) to obtain a cobalt oxide (Co₃O₄). The obtained cobalt oxidehad an average particle diameter of about 5.4 μm.

The obtained cobalt oxide and lithium carbonate were dry-mixed in amolar ratio of Co:Li of about 1:1.04 with a mixer for about 5 minutes,and then thermally treated at about 1,100° C. for about 10 hours (secondthermal treatment). After the second thermal treatment, the resultingproduct was ground by jet milling at about 2,000 rpm, followed by apost-treatment to remove residual lithium and then sieving, therebyobtaining a lithium cobalt oxide (LiCoO₂).

Manufacture Example 1

A coin cell was manufactured using the lithium cobalt oxide (LiCoO₂)prepared in Example 1.

96 g of the lithium cobalt oxide (LiCoO₂) prepared in Example 1, 2 g ofpolyvinylidene fluoride, 47 g of N-methylpyrrolidone as a solvent, and 2g of carbon black as a conducting agent were mixed with a mixer toprepare a uniformly dispersed slurry for forming a positive activematerial layer.

The prepared slurry was coated on an aluminum foil using a doctor bladeto form a thin electrode plate. The electrode plate was then dried atabout 135° C. for about 3 hours, followed by roll pressing and vacuumdrying, thereby manufacturing a positive electrode.

A 2032-type coin cell was manufactured using the positive electrode anda lithium metal counter electrode. While a porous polyethylene (PE) filmseparator (having a thickness of about 16 μm) was disposed between thepositive electrode and the lithium metal counter electrode, anelectrolyte was injected thereinto, thereby obtaining the 2032-type coincell.

The electrolyte was a 1.1 M LiPF₆ solution in a mixed solvent ofethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volumeratio of about 3:5.

Manufacture Example 2

A coin cell was manufactured in the same manner as in ManufactureExample 1, except that the lithium cobalt oxide (LiCoO₂) prepared inExample 2 was used instead of the lithium cobalt oxide (LiCoO₂) preparedin Example 1.

Comparative Manufacture Example 1

A coin cell was manufactured in the same manner as in ManufactureExample 1, except that the lithium cobalt oxide (LiCoO₂) prepared inComparative Example 1 was used instead of the lithium cobalt oxide(LiCoO₂) prepared in Example 1.

Evaluation Example 1: X-Ray Diffraction (XRD) Analysis

The cobalt oxides (Co₃O₄) prepared in Example 1 and Comparative Example1 were analyzed by X-ray diffraction (XRD). The analysis results areshown in FIGS. 2A and 2B.

Referring to FIG. 2A, the cobalt oxide of Example 1 was found to have anabout 1:1 intensity ratio of a second peak at 2θ of about 31.3° to afirst peak at 2θ of about 19° in its X-ray diffraction spectra.Meanwhile, as shown in FIG. 2B, the cobalt oxide of Comparative Example1 had an about 1:2 intensity ratio of a first peak at 2θ of about 19° toa second peak at 2θ of about 31.3° in its X-ray diffraction spectra.These results indicate that the cobalt oxide of Example 1 had adifferent intensity ratio of the second peak to the first peak from thatof the cobalt oxide of Comparative Example 1. Parameters analyzed byX-ray diffraction are shown in Table 1.

TABLE 1 Sample a(Å) x(O) = y(O) = z(O) Co²⁺ (tet) Co³⁺ (oct) R_(B)Example 1 8.0821 0.2617 0.480 1.072 8.8 Comparative 8.0811 0.2613 0.5101.023 7.8 Example 1

In Table 1, R_(B) indicates a fitting accuracy of XRD patterns, “a”denotes the a-axis inside the structure, x(O)=y(O)=z(O) indicates anoxygen coordinate value in the structure, and “oct” is an abbreviationfor octahedral, and “tet” for tetrahedral.

Referring to Table 1, the cobalt oxide of Example 1 was found to includemore Co³⁺ (oct) than Co²⁺ (tet) and have an atomic ratio of about 1:2.23of Co²⁺ (tet) to Co³⁺ (oct), while the cobalt oxide of ComparativeExample 1 had an atomic ratio of about 1:2 of Co²⁺ (tet) to Co³⁺ (oct).

Evaluation Example 2: Pellet Density and Electrode Density

The pellet densities of the lithium cobalt oxide prepared in Example 1and the lithium cobalt oxide prepared in Comparative Example 1 wereanalyzed using a pellet density tester. The results are shown in Table2. The pellet density was determined by measuring the density of thecathode active material having a pellet shape obtained by applying 3 gof the cathode active material into a circular mold having a diameter of1.273 cm and applying a pressure of 1500 kgf/cm² to the mass per volumeof the cathode active material.

TABLE 2 Example Pellet density (g/cm³) Example 1 3.98 ComparativeExample 1 3.87

Referring to Table 2, the lithium cobalt oxide prepared in Example 1 hadan increased pellet density, compared to the lithium cobalt oxideprepared in Comparative Example 1.

Densities of the positive electrodes manufactured in Manufacture Example1 and Comparative Manufacture Example 1 were measured. The results areshown in Table 3 and FIG. 3. The density of the negative electrode iscalculated by dividing the weight of the anode by the negative electrodevolume.

TABLE 3 Example Positive electrode density (g/cm³) Manufacture Example 14.09 Comparative Manufacture 4.00 Example 1

Referring to Table 3 and FIG. 3, the positive electrode manufactured inManufacture Example 1 had an improved density, compared to the positiveelectrode manufactured in Comparative Manufacture Example 1.

Evaluation Example 3: Charge-Discharge Test (Initial Charge andDischarge Efficiency and Capacity Retention)

Charge and discharge characteristics of the coin cells manufactured inManufacture Example 1 and Comparative Manufacture Example 1 wereevaluated using a charger/discharger under the following conditions: Thecoin cells of Manufacture Example 1 and Comparative Manufacture Example1 were each charged at a constant current of 0.1 C rate at 25° C. untilthe voltage reached 4.5 V (vs. Li) and then, while maintaining aconstant voltage of 4.5 V, the charging process was cut off at a currentof 0.05 C rate. Subsequently, each coin cell was discharged with aconstant current of 0.1 C rate until the voltage reached 3.0 V (vs. Li)(formation operation, 1^(st) cycle).

Each coin cell after the 1^(st) cycle of the formation operation wascharged at a constant current of 0.2 C rate at 25° C. until the voltagereached 4.5 V (vs. Li) and then, while maintaining a constant voltage of4.5 V, the charging process was cut off at a current of 0.05 C rate.Subsequently, each coin cell was discharged at a constant current of 0.2C rate until the voltage reached 3.0 V (vs. Li) (formation operation,2^(nd) cycle).

Each coin cell after the 2^(nd) cycle of the formation operation wascharged at a constant current of 1.0 C rate at 25° C. until the voltagereached 4.5 V (vs. Li) and then, while maintaining a constant voltage of4.5 V, the charging process was cut off at a current of 0.05 C rate.Subsequently, each coin cell was discharged at a constant current of 1.0C rate until the voltage reached 3.0 V (vs. Li), and this cycle ofcharging and discharging was repeated 50 times.

The initial charge/discharge efficiency was calculated using Equation 1.The results are shown in Table 4.Initial charge/discharge efficiency(ICE)[%]=[1^(st) cycle dischargecapacity/1^(st) cycle charge capacity]×100   [Equation 1]

A capacity retention with respect to the number of cycles of the coincell manufactured in Manufacture Example 1 is shown in FIG. 5.

TABLE 4 Charge capacity Discharge capacity Example (mAh/g) (mAh/g) I.C.E(%) Manufacture Example 1 223 219 98 Comparative Manufacture 220 216 98Example 1

Referring to Table 4, the coin cell of Manufacture Example 1 was foundto have nearly same initial efficiency characteristics as the coin cellof Comparative Manufacture Example 1.

Referring to FIG. 5, the coin cell of Manufacture Example 1 was found tohave good capacity retention.

Evaluation Example 4: Rate Characteristics

Each of the coin cells manufactured in Manufacture Examples 1 and 2 andComparative Manufacture Example 1 was constant-current charged at a rateof 0.1 C until the voltage reached 4.5 V and then, the coin cells wereconstant-current discharged at a rate of 0.1 C until the voltage reached3.0 V.

During a 2^(nd) cycle, the coin cells were constant-current charged at arate of 0.5 C until the voltage reached 4.5 V, and then, while thevoltage maintained at 4.5 V, the coin cells were constant-voltagecharged until the current reached 0.05 C and then, at a rate of 0.2 C,the coin cells were constant-current discharged until the voltagereached 3.0 V.

During a 3^(rd) cycle, the coin cells were constant-current charged at arate of 0.5 C until the voltage reached 4.5 V, and then, while thevoltage maintained at 4.5 V, the coin cells were constant-voltagecharged until the current reached 0.05 C and then, at a rate of 1.0 C,the coin cells were constant-current discharged until the voltagereached 3.0 V.

During a 4^(th) cycle, the coin cells were constant-current charged at arate of 0.5 C until the voltage reached 4.5 V, and then, while thevoltage maintained at 4.5 V, the coin cells were constant-voltagecharged until the current reached 0.05 C and then, at a rate of 2.0 C,the coin cells were constant-current discharged until the voltagereached 3.0 V.

The rate characteristics of the coin cells of Manufacture Example 1 andComparative Manufacture Example 1 are shown in Table 5.

The rate characteristics of Table 5 were calculated using Equations 2and 3.Rate characteristics(1C/0.1C)(%)=(discharging capacity in 3^(rd)cycle)/(discharging capacity in 1^(st) cycle)×100   [Equation 2]Rate characteristics(2C/0.2C)(%)=(discharging capacity in 4^(th)cycle)/(discharging capacity in 2^(nd) cycle)×100   [Equation 3]

TABLE 5 Rate characteristics Rate characteristics (1 C/0.1 C) (2 C/0.2C) Example (%) (%) Manufacture Example 1 88 85 Comparative Manufacture86 83 Example 1

Referring to Table 5, the coin cell manufactured in Manufacture Example1 was found to have improved rate characteristics, compared to the coincell of Comparative Manufacture Example 1.

Evaluation Example 5: Scanning Electron Microscopy (SEM)

The cobalt oxides prepared in Example 1 and Comparative Example 1 wereanalyzed by scanning electron microscopy (SEM). FIGS. 5A to 5Cillustrate SEM images of the cobalt oxide of Example 1, and FIGS. 6A and6B illustrate SEM images of the cobalt oxide of Comparative Example 1.

Referring to the SEM images of the two cobalt oxides, the cobalt oxideof Example 1 was found to have a different shape from that of the cobaltoxide prepared in Comparative Example 1. The cobalt oxide of Example 1was found to have a needle-like primary particle shape, including spots,and a spherical secondary particle shape having a particle diameter ofabout 15 μm to about 17 μm.

Evaluation Example 6: Particle Size Distribution Test

1) Cobalt Oxide

Particle size distributions of the cobalt oxides prepared in Example 1and Comparative Example 1 were analyzed by dynamic light scattering. Toevaluate the particle size distribution, D10, D90, and D50 werecalculated on a volume basis of particles by dry laser diffractionparticle size analysis. The results of the particle size distributionanalysis are shown in Table 6.

TABLE 6 Example D10 (μm) D90 (μm) D50 (μm) tap density (g/cm³) Example 16.73 23.3 16.2 2.9 Comparative 2.6 8.8 5.4 1.7 Example 1

Referring to Table 6, the cobalt oxide of Example 1 was found to have alarger average particle diameter (D50) and a larger tap density,compared to the cobalt oxide of Comparative Example 1.

2) Lithium Cobalt Oxide

Particle size distributions of the lithium cobalt oxides prepared inExample 1 and Comparative Example 1 were analyzed by dynamic lightscattering. To evaluate the particle size distribution, D10, D90, andD50 were calculated on a volume basis of particles by dry laserdiffraction particle size analysis. The results of the particle sizedistribution analysis are shown in Table 7.

TABLE 7 D10 D90 D50 Example (μm) (μm) (μm) Example 1 12.1 37.6 23Comparative Example 1 8.5 34.18 17.93

Referring to Table 7, the lithium cobalt oxide of Example 1 was found tohave a larger average particle diameter (D50), compared to the lithiumcobalt oxide of Comparative Example 1.

As described above, according to the one or more embodiments, a lithiumcobalt oxide with improved density may be prepared using a cobalt oxideaccording to an embodiment. An electrode containing the lithium cobaltoxide may have improved density characteristics. A lithium secondarybattery with improved lifetime characteristics and rate characteristicsmay be manufactured using the electrode.

By way of summation and review, lithium cobalt oxide has high energydensity per volume, and thus may be used as a positive active material.To further improve the capacity of lithium cobalt oxide, lithium cobaltoxide may have increased density.

The embodiments may provide a cobalt oxide with improved density for usein a lithium secondary battery.

The embodiments may provide a lithium cobalt oxide formed from thecobalt oxide, and a lithium secondary battery having improved cellperformance by including a positive electrode containing the lithiumcobalt oxide.

Example embodiments have been disclosed herein, and although specificterms are employed, they are used and are to be interpreted in a genericand descriptive sense only and not for purpose of limitation. In someinstances, as would be apparent to one of ordinary skill in the art asof the filing of the present application, features, characteristics,and/or elements described in connection with a particular embodiment maybe used singly or in combination with features, characteristics, and/orelements described in connection with other embodiments unless otherwisespecifically indicated. Accordingly, it will be understood by those ofskill in the art that various changes in form and details may be madewithout departing from the spirit and scope of the present invention asset forth in the following claims.

What is claimed is:
 1. A lithium cobalt oxide for a lithium secondarybattery, the lithium cobalt oxide being represented by Formula 1 andhaving: a spherical particle shape, a pellet density of about 3.98 g/ccto about 4.2 g/cc, an average particle diameter (D50) of about 23 μm toabout 28 μm, a particle diameter (D90) of about 35 μm to about 45 μm,and a particle diameter (D10) of about 10 μm to about 13 μm:Li_(a)Co_(b)O_(c)   [Formula 1] wherein, in Formula 1, 0.9≤a≤1.1,0.98≤b≤1.00, and 1.9≤c≤2.1.
 2. The lithium cobalt oxide as claimed inclaim 1, further comprising at least one selected from magnesium (Mg),calcium (Ca), strontium (Sr), titanium (Ti), zirconium (Zr), boron (B),aluminum (Al), and fluorine (F).
 3. A lithium secondary batterycomprising a positive electrode that includes the lithium cobalt oxideas claimed in claim
 1. 4. The lithium secondary battery as claimed inclaim 3, wherein the positive electrode has a density of about 4.05 g/ccto about 4.15 g/cc.